Affinity spectrum approach

A variety of alternative models more realistic than the Langmuir isotherm may be used to fit the isotherm data the most accurate but most demanding (in terms of amount and accuracy of data required) is the affinity spectrum approach, which yields a continuous spectrum of number of binding sites vs. [27]. The simplest approach, however, is to model the isotherm as resulting from just two classes of binding site ... 

A common method of extracting f K) from Eq. 3.82 is to assume a form of the distribution function by differentiation of a smooth fimction describing the data. The function obtained by this method is called the affinity spectrum (AS) and the method, the AS method [71]. The most general approach uses a cubic spline to approximate the data. However, a simpler procedure uses a Langmuir-Freundlich (LF) isotherm model and the AS distribution is derived from the best parameters of a fit of the experimental isotherm data to the LF model [71]. This approach yields a unimodal distribution of binding affinity with a central peak, if the range... 

A recent model, based on the Donnan equilibrium concept, but with a different approach, is the elastic polyelectrolyte network (EPN) model. In the EPN model (Orsetti, Andrade, and Molina 2010), the HS particles are considered as divided in to two fractions an inner fraction gf, which behaves as a gel in Donnan equilibrium with the bulk solution, and an external fraction 1-g/, which is in equilibrium with the bulk (Figure 13.8) thus, it is assumed that a fraction gf of the total number of sites resides inside the gel phase, whereas a fraction f-g/ resides outside the gel given an affinity spectrum, it applies to the external sites in equilibrium with the bulk solutions, with activity a for ion i, whereas for the internal medium, it is applied the internal activity aP, in Donnan equilibrium with the bulk ... 

One distinct advantage of this system, i.e., the use of the MIANS label in conjunction with the anti-MIANS affinity column, over a similar approach, e.g., using the biotin-avidin interaction, is that the MIANS label can be tracked at a wavelength, approximately 320 nm, which is unique from the peptide or protein absorbance spectrum (Gupte and Leine, 1979 Andley et al., 1986). Another potential advantage is that the anti-MIANS colunm is reusable. The column has been routinely regenerated for multiple uses. 

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